The present invention relates to liquid transport members useful for a wide range of applications requiring high flow and/or flux rate, wherein the liquid can be transported through such a member, and/or be transported into or out of such a member. Such members are suitable for many applications, asxe2x80x94without being limited toxe2x80x94disposable hygiene articles, water irrigation systems, spill absorbers, oil/water separators and the like. The invention further relates to liquid transport systems comprising said liquid transport members and articles utilizing these.
The need to transport liquids form one location to another is a well known problem.
Generally, the transport will happen from a liquid source through a liquid transport member to a liquid sink, for example from a reservoir through a pipe to another reservoir. There can be differences in potential energy between the reservoirs (such as hydrostatic height) and there can be frictional energy losses within the transport system, such as within the transport member, in particular if the transport member is of significant length relative to the diameter thereof.
For this general problem of liquid transport, there exist many approaches to create a pressure differential to overcome such energy differences or losses so as to cause the liquids to flow. A widely used principle is the use of mechanical energy such as pumps. Often however, it will be desirable to overcome such energy losses or differences without the use of pumps, such as by exploiting hydrostatic height differential (gravity driven flow), or via capillary effects (often referred to as wicking).
In many of such applications, it is desirable to transport the liquids at high rates, i.e. high flow rate (volume per time), or high flux rate (volume per time per unit area of cross-section).
Examples for applications of liquid transport elements or members can be found in fields like water irrigation such as described in EP-A-0.439.890, or in the hygiene field, such as for absorbent articles like baby diapers both of the pull-on type or with fastening elements like tapes, training pants, adult incontinence products, feminine protection devices.
A well known and widely used execution of such liquid transport members are capillary flow members, such as fibrous materials like blotting paper, wherein the liquid can wick against the gravity. Typically such materials are limited in their flow and/or flux rates, especially when wicking height is added as an additional requirement. An improvement particularly towards high flux rates at wicking heights particularly useful for example for application in absorbent articles has been described in EP-A-0.810.078.
Other capillary flow members can be non-fibrous, but yet porous structures, such as open celled foams. In particular for handling aqueous liquid, hydrophilic polymeric foams have been described, and especially hydrophilic open celled foams made by the so called High Internal Phase Emulsion (HIPE) polymerization process have been described in U.S. Pat. No. 5,563,179 and U.S. Pat. No. 5,387,207.
However, in spite of various improvements made on such executions, there is still a need to get significant increase in the liquid transport properties of liquid transport members.
In particular, it would be desired to obtain liquid transport members, that can transport liquid against gravity at very high flux rates.
In situations wherein the liquid is not homogeneous in composition (such as a solution of salt in water), or in its phases (such as a liquid/solid suspension), it can be desired to transport the liquid in its totality, or only parts thereof. Many approaches are well known for their selective transport mechanism, such as in the filter technology.
For example, filtration technology exploits the higher and lower permeability of a member for one material or phase compared to another material or phase. There is abundance of art in this field, in particular also relating to the so called micro-, ultra-, or nano-filtration. Some of the more recent publications are:
U.S. Pat. No. 5,733,581 relating to melt-blown fibrous filter;
U.S. Pat. No. 5,728,292 relates to non-woven fuel filter;
WO-A-97/47375 relating to membrane filter systems;
WO-A-97/35656 relating to membrane filter systems;
EP-A-0.780.148 relating to monolithic membrane structures;
EP-A-0.773.058 relating to oleophilic filter structures.
Such membranes are also disclosed to be used in absorbent systems.
In U.S. Pat. No. 4,820,293 (Kamme) absorbent bodies are disclosed, for being used in compresses, or bandages, having a fluid absorbent substance enclosed in a jacket made of one essentially homogeneous material. Fluid can enter the body through any part of the jacket, and no means is foreseen for liquid to leave the body.
Therein, fluid absorbent materials can have osmotic effects, or can be gel-forming absorbent substances enclosed in semipermeable membranes, such as cellulose, regenerated cellulose, cellulose nitrate, cellulose acetate, cellulose acetate butyrate, polycarbonate, polyamide, fiberglass, polysulfone, of polytetrafluoroethylene, having pore sizes of between 0.001 xcexcm and 20 xcexcm, preferably between 0.005 xcexcm and 8 xcexcm, especially about 0.01 xcexcm.
In such a system, the permeability of the membrane is intended to be such that the absorbed liquid can penetrate, but such that the absorbent material is retained.
It is therefore desired to use membranes having a high permeability K and a low thickness d, so as to achieve a high liquid conductivity k/d of the layer, as being described herein after.
This can be achieved by incorporation of promoters with higher molecular weight (e.g., polyvinyl pyrrolidone with a molecular weight of 40,000), such that the membranes can have larger pores leading to larger membrane permeability k. The maximum pore size stated therein to be useful for this application is less than 0.5 xcexcm, with pore sizes of about 0.01 xcexcm or less being preferred. The exemplified materials allow the calculation of kid values in the range of 3 to 7*10xe2x88x9214 m.
As this system is quite slow, the absorbent body can further comprise for rapid discharge of fluids a liquid acquisition means, such as conventional acquisition means to provide interim storage of the fluids before these are slowly absorbed.
A further application of membranes in absorbent packets is disclosed in U.S. Pat. No. 5,082,723, EP-A-0.365.565, or U.S. Pat. No. 5,108,383 (White; Allied-Signal).
Therein, an osmotic promoter, namely a high-ionic strength material such as NaCl, or other high osmolality material like glucose or sucrose is placed inside a membrane such as made from cellulosic films. As with the above disclosure, fluid can enter the body through any part of the jacket, and no means. is foreseen for liquid to leave the body. When these packets are contacted by aqueous liquids, such as urine, the promoter materials provide an osmotic driving force to pull the liquid through the membranes. The membranes are characterized by having a low permeability for the promoter, and the packets achieve typical rates of 0.001 ml/cm2/min. When calculating membrane conductivity k/d values for the membranes disclosed therein, values of about 1 to 2*10xe2x88x9215 m result. An essential property of membranes useful for such applications is their xe2x80x9csalt retentionxe2x80x9d, i.e. whilst the membranes should be readily penetrable by the liquid, they must retain a substantial amount of the promoter material within the packets. This salt retention requirements provides a limitation in pore size which will limit liquid flux.
U.S. Pat. No. 5,082,723 (Gross et al.) discloses an osmotic material like NaCl which is enclosed by superabsorbent material, such as a copolymer of acrylic acid and sodium acrylate, thereby aiming at improving absorbency, such as enhanced absorptive capacity on a xe2x80x9cgram per gramxe2x80x9d basis and absorption rate.
Overall, such fluid handling members are used for improved absorbency of liquids, but have only very limited fluid transport capability.
Thus, there remains still a need to improve the liquid transport properties, in particular to increase the flow and/or flux rates in liquid transport systems.
Hence it is an object of the present invention to provide a liquid transport member composed of at least two regions exhibiting a difference in permeability.
It is a further object to provide liquid transport members exhibiting improved liquid transport, as expressed in significantly increased liquid flow rates, and especially liquid flux rates, i.e. the amount of liquid flowing in a time unit through a certain cross-section of the liquid transport member.
It is a further object of the present invention to allow such liquid transport against gravity.
It is a further object of the present invention to provide such an improved liquid transport member for fluids with a wide range of physical properties, such as for aqueous (hydrophilic) or non-aqueous, oily or lipophilic liquids.
It is a further object of this invention to provide liquid transport systems, comprising in addition to the liquid transport member a liquid sink and/or liquid source.
It is an even further object of the present invention to provide any of the above objects for being used in absorbent structures, such as can be useful in hygienic absorbent products, such as baby diapers, adult incontinence products, feminine protection products.
It is an even further object of the present invention to provide any of the above objects for use as water irrigation systems, spill absorber, oil absorber, water/oil separators.
The present invention is a liquid transport member having at least one bulk region with an average permeability kb, and a wall region that completely circumscribes said bulk region, whereby the wall region further comprises at least one port region having a thickness d and an average permeability kp throughout this thickness, whereby the bulk region has an average fluid permeability kb which is higher than the average fluid permeability kp of the port region and that said port region has a ratio of fluid permeability to thickness in the direction of fluid transport, kp/dp of at least 10xe2x88x927 m. Preferably, the bulk region has a fluid permeability of at least 10xe2x88x9211 m2, preferably at least 10xe2x88x928 m2, more preferably at least 10xe2x88x927 m2, most preferably at least 10xe2x88x925 m2, but preferably of not more than 10xe2x88x922 m2. In another preferred embodiment, the said port region has a fluid permeability of at least 6*10xe2x88x9220 m2, preferably at least 7*10xe2x88x9218 m2, more preferably at least 3*10xe2x88x9214 m2, even more preferably of at least 1.2*10xe2x88x9211 m2, or even at least 7*10xe2x88x9211 m2, most preferably at least 10xe2x88x929 m2, or a ratio of fluid permeability to thickness in the direction of fluid transport, kp/dp of at least 5*10xe2x88x927 m, preferably at least 10xe2x88x926 m, preferably at least 10xe2x88x925 m.
In a further preferred embodiment of the present invention, the bulk region has an average dry density of more than 0.001 g/cm3.
In a particular aspect of the invention, the liquid transport member comprises a first material in a first region, and wherein the member further comprises an additional element in contact with the first materials of the first region which extends into a neighbouring second region of said liquid transport member that is in contact with the wall region. The additional element can be in contact with the wall region and can extend into the neighbouring second region, and can have a capillary pressure for absorbing the liquid that is lower than the bubble point pressure of the liquid transport member. The additional element can comprise a softness layer.
In a further aspect of the invention, the ratio of permeability of the bulk region to the permeability of the port region of the liquid handling member is at least 10, preferably at least 100, more preferably at least 1000, and even more preferably at least 100,000. The liquid handling member can exhibit a bubble point pressure when measured with water having a surface tension of 72 mN/m of at least 1 kPa, preferably at least 2 kPa, more preferably at least 4.5 kPa, even more preferably 8 kPa, most preferably 50, and the port region of the member can exibit a a bubble point pressure when measured with water having a surface tension of 72 mN/m of at least 1 kPa, preferably at least 2 kPa, more preferably at least 4.5 kPa, even more preferably 8 kPa, most preferably 50 and when measured with an aqueous test solution having a surface tension of 33 mN/m of at least 0.67 kPa, preferably at least 1.3 kPa, more preferably at least 3.0 kPa, even more preferably 5.3 kPa, most preferably 33 kPa.
In yet a further aspect, a liquid transport member according to the present invention can loose more than 3% of the initial liquid when submitted to the closed system test.
A liquid transport member can have a bulk region which has a larger average pore size than said port region, preferably such that the ratio of average pore size of the bulk region and the average pore size of the port region is at least 10, preferably at least 50, more preferably at least 100, and even more preferably at least 500, and most preferably at least 350, and the bulk region can have an average pore size of at least 200 xcexcm, preferably at least 500 xcexcm, more preferably of at least 1000 xcexcm, and most preferably of at least 5000 xcexcm, or a porosity of at least 50%, preferably at least 80%, more preferably at least 90%, even more preferably of at least 98%, and most preferably of at least 99%. In a further aspect, the port region can have a porosity of at least 10%, preferably at least 20%, more preferably of at least 30%, and most preferably of at least 50%, or an average pore size of no more than 100 xcexcm, preferably no more than 50 xcexcm, more preferably of no more than 10 xcexcm, and most preferably of no more than 5 xcexcm, but preferably not less than 1 xcexcm, preferably at least 3 xcexcm. Further, the port region can have an average thickness of no more than 100 xcexcm, preferably no more than 50 xcexcm, more preferably of no more than 10 xcexcm, and most preferably of no more than 5 xcexcm. The bulk region and the wall region can have a volume ratio of at least 10, preferably at least 100, more preferably at least 1000, and even more preferably at least 100,000.
In yet a further embodiment, the port region is hydrophilic, preferably by having a receding contact angle for the liquid to be transported of less than 70 degrees, preferably less than 50 degrees, more preferably less than 20 degrees, and even more preferably less than 10 degrees. In a particular embodiment, the port region does not reduce the surface tension of the transported liquid. In a further embodiment, the port region is oleophilic, preferably by having a receding contact angle for the liquid to be transported of less than 70 degrees, preferably less than 50 degrees, more preferably less than 20 degrees, and even more preferably less than 10 degrees.
In yet another aspect of the present invention, the liquid transport member or the bulk region thereof comprises a material which is expandable upon liquid contact and collapsible upon liquid removal, preferably by a volume expansion factor of at least 5.
A liquid transport member according to the present invention can be sheet-like shape, or has a cylindrical like shape, or can have a cross-section area along the direction of liquid transport is not constant. The port region of the the member preferably have a larger area than the average cross-section of the member along the direction of liquid transport, preferably by at least a factor of 2, preferably a factor of 10, most preferably a factor of 100.
The bulk region of a liquid transport member can comprise material selected from the groups of fibers, particulates, foams, spirals, films, corrugated sheets, or tubes, and the wall region can comprise material selected from the groups of fibers, particulates, foams, spirals, films, corrugated sheets, tubes, woven webs,woven fiber meshes, apertured films, or monolithic films. The foam can be an pen cell reticulated foam, preferably selected from the group of cellulose sponge, polyurethane foam, HIPE foams, and the fibers can be made of polyolefins, polyesters, polyamids, polyethers, polyacrylics, polyurethanes, metal, glass, cellulose, cellulose derivatives.
A liquid transport member can comprise a porous bulk region that is wrapped by a separate wall region. It also can comprise soluble materials, such as in the port region. The membranes in the port region can comprise stimulus activatable membrane materials, such as a membrane, which changes its hydrophilicity upon a temperature change.
The liquid transport member can be initially partially or essentially filled with liquid., or it can be initially under vacuum.
In a further aspect of the present invention, the liquid transport member is suitable for the transport of water-based liquids or of viscoelastic liquids, of bodily discharge fluids, as urine, blood menses, sweat or feces, or of oil, grease, or other non-water based liquids. Such a transport can be also selective, such as for oil or grease, but not water based liquids.
I yet a further aspect, a liquid transport can exhibit properties or parameter which are established prior to or at the liquid handling, preferably by activation by contact with the liquid, pH, temperature, enzymes, chemical reaction, salt concentration or mechanical activation.
In yet a further aspect, the present invention relates to a liquid transport system having a liquid transport member as described in the above, in addition to a source or sink of liquid, each of the sink or source possibly being outside or inside of the member. Such a system can exhibit an absorbent capacity of at least 5 g/g, preferably at least 10 g/g, more preferably at least 50 g/g on the basis of the weight of the said system, when submitted to the Demand Absorbency Test. Such a system can comprise materials in the sink, which have an absorption capacity in the teabag test of at least 10 g/g, preferably at least 20 g/g and more preferably at least 50 g/g on the basis of the weight of the sink material. The sink material can also exhibit an absorbent capacity of at least 5 g/g, preferably of at least 10 g/g, more preferably of at least 50 g/g on the basis of the weight of the sink material, when measured in the Capillary Sorption Test at a pressure up to the bubble point pressure of the port region, and which has an absorbent capacity of at less than 5 g/g, preferably of less than 2 g/g, more preferably of less than 1 g/g and most preferably of less than 0.2 g/g, when measured in the Capillary Sorption Test at a pressure exceeding the bubble point pressure of the port region. A system can comprise superabsorbent material or open celled foam of the High Internal Phase Emulsion (HIPE) type.
In yet a further aspect, the invention is concerned with an article including a liquid transport member or system. Such an article can be a baby or adult incontinence diaper, a feminine protection pad, a pantiliner, or a training pant, or a grease absorber, or a water transport member.
In yet a further aspect, the present invention is concerned with the method of making a liquid transport member, comprising the steps of a) providing a bulk region material or a void space; b) providing a wall material comprising a port region; c) completely enclosing said bulk region material or said void space by said wall material; d) providing a transport enablement means selected from d1) vacuum; d2) partial or essentially complete liquid filling; d3) expandable elastics/springs. The method can further comprise the step of applying activation means, such as e1) a liquid dissolving port region; e2) a liquid dissolving expandable elastication/springs; e3) a removable release element; or e4) a removable sealing packaging. Alternatively, the method can comprise the steps of a) wrapping a highly porous bulk material with a separate wall material that comprises at least one permeable port region, b) completely sealing the wall region, and c) evacuating the member essentially of air, optionally filling the member with liquid.